The present invention relates to oximeter sensors and, in particular, oximeter sensors with a heating element to improve perfusion.
Pulse oximetry is typically used to measure various blood characteristics including, but not limited to, the blood-oxygen saturation of hemoglobin in arterial blood, and the rate of blood pulsations corresponding to the heart rate of a patient. Measurement of these characteristics has been accomplished by use of a noninvasive sensor which passes light through a portion of the patient's tissue where blood perfuses the tissue, and photoelectrically senses the absorption of light in such tissue. The amount of light absorbed is then used to calculate the amount of blood constituent being measured.
The light passed through the tissue is selected to be of one or more wavelengths that are absorbed by the blood in an amount representative of the amount of the blood constituent present in the blood. The amount of transmitted or reflected light passed through the tissue will vary in accordance with the changing amount of blood constituent in the tissue and the related light absorption. For measuring blood oxygen level, such sensors have been provided with light sources and photodetectors that are adapted to operate at two different wavelengths, in accordance with known techniques for measuring blood oxygen saturation.
Heaters have been used in sensors to improve the perfusion, or amount of blood, adjacent the sensor. This will improve the measurement since the light will encounter a larger volume of blood, giving a better signal-to-noise ratio for the oximeter reading.
Because the normal human body core temperature is approximately 37° C., and burning of tissue could take place for temperatures above approximately 42–43° C., a tight range of control of the heating element is required. Although heating devices can be designed to automatically control the temperature of the sensor and hence the patient's tissue, there exists a need for a simple, low cost and effective way of assuring the operator of such a device that the warming feature of the sensor is correctly functioning. Moreover, in cases of nonheated sensors, a need also exists for a simple, low cost and effective way of indicating a degree of tissue perfusion by showing the temperature of a particular tissue location in contact with the sensor.